Hodgdon Benchmark
This is our top pick for 55 grain bullets.  Our favorite load of all time is 55 grain Sierra Blitzking and 25.0 grains of Benchmark at 2.255 OAL using Federal AR Match primers, and that brass.  It shoots lights out in any AR ever tried we own.

Notice some say "tip smashed?  The bullet seating die put deep rings in many bullets, then I changed the seating stem and the ones say Tip normal, are perfect.  Notice there is almost no difference at 50 yards.